Lubricant compositions for transmissions

ABSTRACT

Transmission lubricant compositions comprise a mineral oil as a base oil of which % CP and % CA defined in ASTM D 3238 are 70 or more and 3 or less, respectively, a viscosity index improver, and a friction modifier. The transmission lubricant compositions have excellent low temperature fluidity, shear stability, and durability of anti-shudder properties and thus can be used for extended periods of time.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to lubricant compositions fortransmissions, and more particularly to lubricant compositions which arefree from a reduction in anti-shudder properties even after prolongeduse. The lubricant compositions are particularly useful for automatictransmissions and continuously variable transmissions.

[0003] 2. Description of the Prior Art

[0004] In recent years, with the objective of the cost reduction of oilchanges and the reduction of the amount of waste oil, a demand hasarisen for transmission lubricant compositions which have long durationof life and can maintain their properties even after the long-time use.

[0005] In addition to automatic transmissions, most of continuouslyvariable transmissions are equipped with a torque converter. Recently,lock-up clutches have been built in torque converters as effective meansto improve mileage such that in addition to power transmission vialubricant, the engine torque is directly transmitted to thetransmission. However, a torque converter clutch works only in ahigh-speed range where the engine torque fluctuations are less when thetorque converter works in a low-speed range, the engine torquefluctuations bring about abnormal vibration of the car body, leading tounpleasant driving conditions. As a result, in the low-speed range,e.g., during the starting period, power transmission loss occurs, causedby a difference between the input and output revolutions, i.e., engineoutput and transmission input, leading to a decrease in gas mileage.

[0006] In order to decrease such power transmission loss, a slip controlmechanism is used in some automobiles in which the torque converterworks at a low speed range and the engine torque fluctuation is absorbedby the relative slip of the clutch. However, in such a case, there is apossibility that abnormal vibration of the car body, so-called shudderoccurs at the torque converter clutch's surface, resulting inuncomfortable riding conditions. In order to prevent the occurrence ofshudder, the lubricant is required to have improved μ (frictioncoefficient)-V(sliding velocity) properties such that the frictioncoefficient is increases as sliding velocity increases. The use offriction modifiers is effective to improve the μ-V properties and thusmany friction modifiers have been proposed. However, there has not beenobtained a satisfactory result with regard to long-lasting anti-shudderproperties.

[0007] The transmission lubricants must maintain proper viscosity tolubricate a gear shaft bearing mechanism and particularly those used ina transmission having a hydraulic controlling mechanism are required tomaintain proper viscosity so as to prevent it from leaking from thecontrol valve. Furthermore, the transmission lubricant are required tobe less in viscosity reduction even after the use for extended periodsof time. In addition to this, the transmission lubricants are alsorequired to have an excellent low temperature fluidity because theincrease of its resistance to stirring under cold conditions invite thedecrease of gas mileage and therefore, viscosity at low temperatures areimportantly needed to be suppress low.

[0008] In view of the foregoing circumstances, there has been a greatdeal of need to develop a lubricant for transmissions which has inaddition to long-lasting anti-shudder properties excellent lowtemperature fluidity and shear stability.

[0009] It is an object of the present invention to provide transmissionlubricant compositions which have and maintains excellent shearstability and anti-shudder properties for extended periods of timewithout being degraded.

SUMMARY OF THE INVENTION

[0010] According to the present invention, there is provided atransmission lubricant composition comprising a mineral oil as a baseoil hereinafter referred to as Component (A) of which % C_(p) and %C_(A) defined by ASTM D3238 are 70 or more and 3 or less, respectively,as a main component, a viscosity-index improver hereinafter referred toas Component (B), and a friction modifier hereinafter referred to asComponent (C).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention is described below in more details.

[0012] A mineral oil having a % C_(p) of 70 or more and a % C_(A) of 3or less both of which are defined by ASTM D 3238, are used as Component(A) in the present invention.

[0013] Since Component (A) fulfills the conditions of % C_(P)≧70 and %C_(A)≦3, the composition of the present invention exhibits excellent lowtemperature fluidity and long lasting anti-shudder propertiessynergistically with Components (B) and (C).

[0014] No particular limitation is imposed on the kinematic viscosity ofComponent (A). However, Component (A) has a kinematic viscosity of from1 to 10 mm²/s, particularly preferably from 1 to 4 mm²/s. The use of amineral base oil having a kinematic viscosity at 100° C. of 1.0 mm²/S ormore can form oil film and provide lubricity for the lubricantcomposition and moreover can reduce the evaporation loss of the base oilat elevated temperatures. The use of a mineral base oil having akinematic viscosity at 100° C. of 10 mm²/S or less can reduce the flowresistance of itself, resulting in a lubricant composition having alower friction resistance at friction parts. The use of a mineral baseoil having a kinematic viscosity at 100° C. of 4 mm²/S or less canfurther enhance the low temperature fluidity of the resulting lubricantcomposition.

[0015] No particular limitation is imposed on the viscosity index ofComponent (A) as well. However, the viscosity index of Component (A) ispreferably 50 or more and particularly preferably 80 or more. The use ofa base oil having a viscosity index of 50 or more is contributive to theproduction of a lubricant composition which are further superior in thecapabilities of both oil film formation and flow resistance reduction.

[0016] Mineral oils used as Component (A) may be produced any suitablemethod. For example, mineral oils which may be used include paraffinic-and naphthenic- mineral oils which are produced by subjecting lubricantfractions resulting from the atmospheric distillation and vacuumdistillation of crude oil to refining processes such as solventdeasphalting, solvent extraction, hydrocracking, solvent dewaxing,catalytic dewaxing, hydrorefining, sulfuric acid washing, and claytreatment in suitable combination; and n-paraffinic mineral oils.

[0017] More specifically, mineral base oils can be obtained by refiningthe starting oil as it is or the lubricant fractions recovered therefromthrough the usual refining processes and then recovering the lubricantfractions. The starting oil may be (i) distillate oils resulting fromthe atmospheric distillation of a paraffin based crude oil and/or of amixed base crude oil; (ii) distillate oils resulting from the vacuumdistillation of the topped crude of a paraffin based crude oil and/or ofa mixed base crude oil; (iii) oils resulting from mild hydrocracking ofoils (i) and/or (ii); (iv) mixed oils of two or more selected from oils(i), (ii), and (iii); (v) deasphalted oils of oils (i) to (iv), (vi)oils resulting from mild hydrocracking of oils (v); and (vii) mixed oilsof two or more selected from oils (i) to (vi).

[0018] There is no restriction to the usual refining processes mentionedabove which may be any of the refining methods used upon production oflubricant base oils. Specific examples of such refining methods are (a)hydro-refining such as hydrocracking and hydro-finishing; (b) solventrefining such as furfral extraction; (c) dewaxing such as solventdewaxing and catalytic dewaxing; (d) clay treatment with acid clay oractive clay; and (e) acid or alkali chemical refining such as sulfuricacid washing and caustic soda washing. In the production of thelubricant composition of the present invention, the above-describedmethods may be used individually or in combination in any order.Needless to mention, the refining condition of each of the refiningmethods, i.e., the temperature and pressure in the hydro-refining issuitably selected such that a mineral oil having the desired propertiescan be obtained.

[0019] The mineral oils which may be used as Component (A) of thepresent invention can be easily obtained by utilizing preferably 50percent by mass or more, more preferably 70 percent by mass or more,particularly preferably 80 percent by mass or, based on the total massof the base oil, of a component produced by hydrocracking the startingoil selected from the oils (i) to (vii) as it is or the lubricantfraction recovered therefrom; solvent- or catalytic dewaxing theresulting product as it is or the lubricant fraction recoveredtherefrom; and solvent-refining the resulting product or such assolvent- or solvent- or catalytic dewaxing the resulting product afterthe solvent-refining.

[0020] Component (A) may be a mixture of two or more kinds of refinedmineral oils obtained by any of the above-described refining processesor a single refined mineral oil by the same. However, in any case, themineral oils used as Component (A) of the present invention must fulfilsthe conditions of % C_(P)≧70 and % C_(A≦)3. In other words, as long asthey fulfils such conditions, any kind of mineral oils can be used asComponent (A). Therefore, the mineral oils which may be used asComponent (A) may contain small amounts of synthetic oils such aspoly-α-olefins and ester-based synthetic oils.

[0021] Eligible viscosity index improvers, i.e., Component (B) of thepresent invention are non-dispersion type and dispersion type viscosityindex improvers.

[0022] Specific examples of the non-dispersion type- viscosity indeximprovers are polymers or copolymers obtained by polymerizing one ormore monomers represented by formulae (1), (2) and (3) below, andhydrides of these polymers:

[0023] Specific examples of the dispersion type-viscosity indeximprovers are copolymers of two or more monomers selected from the groupconsisting of compounds represented by formulae (4) and (5) below andhydrides thereof and copolymers of one or more monomers selected fromthe group consisting of compounds represented by formulae (1), (2) and(3) above with one or more monomers selected from the group consistingof compounds represented by formulae (4) and (5) below and hydridesthereof

[0024] In formula (1), R¹ is hydrogen or methyl, and R² is an alkylgroup having 1 to 18 carbon atoms.

[0025] Specific examples of the alkyl group having 1 to 18 carbon atomsfor R² are alkyl groups, which may be straight-chain or branched, suchas methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl,decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl,heptadecyl, and octadecyl groups.

[0026] In formula (2), R³ is hydrogen or methyl, and R⁴ is a hydrocarbongroup having 1 to 12 carbon atoms.

[0027] Specific examples of the hydrocarbon group having 1 to 12 carbonatoms are alkyl groups, which may be straight-chain or branched, such asmethyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl,decyl, undecyl, and dodecyl groups; alkenyl groups, which may bestraight-chain or branched and the position of which the double bond mayvary, such as butenyl, pentenyl, hexenyl, heptenyl, octenyl, nonenyl,decenyl, undecenyl, and dodecenyl groups; cycloalkyl groups having 5 to7 carbon atoms, such as cyclopentyl, cyclohexyl, and cycloheptyl groups;alkylcycloalkyl groups, of which the alkyl group may bonded to anyposition of the cycloalkyl group, having 6 to 11 carbon atoms, such asmethylcyclopentyl, dimethylcyclopentyl, methylethylcyclopentyl,diethylcyclopentyl, methylcyclohexyl, dimethylcyclohexyl,methylethylcyclohexyl, diethylcyclohexyl, methylcycloheptyl,dimethylcycloheptyl, methylethylcycloheptyl, and diethylcycloheptylgroups; aryl groups such as phenyl and naphtyl groups; alkylaryl groups,of which the alkyl group may be straight-chain or branched and bond toany position of the aryl group, having 7 to 12 carbon groups, such astolyl, xylyl, ethylphenyl, propylphenyl, butylphenyl, pentylphenyl, andhexylphenyl groups; and phenylalkyl groups, of which the alkyl group maybe straight-chain or branched, having 7 to 12 carbon atoms, such asbenzyl, phenylethyl, phenylpropyl, phneylbutyl, phenylpentyl, andphenylhexyl groups.

[0028] In formula (3), D¹ and D² are each independently hydrogen, aresidue of an alkylalcohol having 1 to 18 carbon atoms represented bythe formula —OR⁵ wherein R⁵is an alkyl group having 1 to 18 carbonatoms, or a residue of a monoalkylamine having 1 to 18 carbon atomsrepresented by the formula—NHR⁶ wherein R⁶ is an alkyl group having 1 to18 carbon atoms.

[0029] Specific examples of the alkyl group for R⁵ and R⁶ are the sameas those exemplified with regard to R² in formula (1).

[0030] Among the monomers of formulae (1), (2), and (3), preferred arealkylacrylates and alkylmethacrylates of formula (1); olefins of formula(2) wherein R³is hydrogen or methyl, and R⁴is an alkyl group having 1 to12 carbon atoms; styrene of formula (2) wherein R³ is hydrogen, and R⁴is phenyl; α-methylstyrene of formula (2) wherein R³ is methyl, and R⁴is phenyl; p-methylstyrene of formula (2) wherein R³is hydrogen, andR⁴is tolyl; maleates of formula (3) wherein D¹ and D² are —OR⁵ whereinR⁵is alkyl; and maleic amides of formula (3) wherein D¹ and D² are —NHR⁶wherein R⁶ is alkyl.

[0031] In formula (4), R⁷ is hydrogen or methyl, R⁸ is an alkylene grouphaving 1 to 18 carbon atoms, E¹ is an amine residue or heterocyclicresidue having 1 or 2 nitrogen and 0 to 2 oxygen, and a is an integer of0 or 1.

[0032] Specific examples of the alkylene group having 1 to 18 carbonatoms for R⁸ are ethylene, propylene, butylene, pentylene, hexylene,heptylene, octylene, nonylene, decylene, undecylene, dodecylene,tridecylene, tetradecylene, pentadecylene, hexadecylene, heptadecylene,and octadecylene groups, all of which may be straight-chain or branched.

[0033] Specific examples of the amine residue for E¹ are dimethylamino,diethylamino, dipropylamino, dibutylamino, anilino, toluidino, xylidino,acetylamino, and benzoilamino. Specific examples of the heterocyclicresidue are morpholino, pyrolyl, pyridyl, methylpydidyl, pyrolidinyl,piperidinyl, quinonyl, pyrrolidonyl, pyrrolidono, imidazolino, andpyrazino groups.

[0034] In formula (5), R⁹ is hydrogen or methyl, and E² is an amineresidue or heterocyclic residue having 1 or 2 nitrogen and 0 to 2oxygen.

[0035] Specific examples of the amine residue for E² are dimethylamino,diethylamino, dipropylamino, dibutylamino, anilino, toluidino, xylidino,acetylamino, and benzoilamino. Specific examples of the heterocyclicresidue are morpholino, pyrolyl, pyridyl, methylpydidyl, pyrolidinyl,piperidinyl, quinonyl, pyrrolidonyl, pyrrolidono, imidazolino, andpyrazino groups.

[0036] Among the monomers of formulae (4), (5), and (6), preferred aredimethylaminomethacrylate of formula (4) wherein R⁷ is methyl, R⁸ ismethylene, and E¹ is dimethylamino; diethylaminomethylmethacrylate offormula (4) wherein R⁷ is methyl, R⁸ is methylene, and E¹ isdiethylamino; dimethylaminoethylmethacrylate of formula (4) wherein R⁷is methyl, R⁸ is ethylene, and E¹ is dimethylamino;diethylaminoethylmethacrylate of formula (4) wherein R⁷ is methyl, R⁸ isethylene, and E¹ is diethylamino; morpholinomethylmethacrylate offormula (4) wherein R⁷ is methyl, R⁸ is methylene, and E¹ is morpholino;morpholinoethylmethacrylate of formula (4) wherein R⁷ is methyl, R⁸ isethylene, and E¹ is morpholino; 2-vinyl-5-methylpyridine of formula (5)wherein R⁹ is hydrogen, and E² is 5-methylpyridyl; andN-vinylpyrrolidone of formula (5) wherein R⁹ is hydrogen and E² ispyrrolidono.

[0037] When one or more monomers represented by formula (1), (2) or (3)is copolymerized with one or more monomers represented by formula (4) or(5), the molar ratio of the former monomers to the latter monomers isarbitrary selected but is within the range of 80:20 to 95:5. Thecopolymerization is conducted using any suitable conventional method byradical-solution polymerization of the monomers in the presence of apolymerization initiator such as benzoyl peroxide.

[0038] Specific examples of Component (B), i.e., viscosity indeximprovers are polymethacrylates, ethylene-α-olefin copolymers andhydrides thereof, polyisobutylene and hydrides thereof, styrene-dienehydrogenated copolymers, styrene-maleic anhydrides copolymers, andpolyalkylstyrene. These viscosity index improvers may be of eitherdispersion type or non-dispersion type. However, preferred aredispersion type viscosity index improvers because of their capability tomaintain anti-shudder properties.

[0039] Preferred for Component (B) are polymethacrylates because theyare superior in an enhancement in low temperature fluidity. Themolecular weight of polymethacrylates is preferably selected in view ofshear stability. In general, preferred polymethacrylates are thosehaving a weight-average molecular weight of 10,000 to 200,000,preferably 10,000 to 60,000 in view of the prolonged use.

[0040] No particular limitation is imposed on the content of Component(B). In general, it is contained in an amount of preferably 0.1 to 25percent by mass, more preferably 0.5 to 20 percent by mass, based on thetotal mass of the transmission lubricant composition. A content ofComponent (B) which is less than 0.1 percent by mass would be poor ineffect to improve low temperature fluidity, while that in excess of 25percent by mass would fail to exhibit an effect corresponding to theamounts.

[0041] Component (C) of the present invention is a friction modifier.Eligible friction modifiers are those having in its molecules at leastone alkyl or alkenyl group having 6 to 30, preferably 9 to 24 carbonatoms and no hydrocarbon group having 31 or more carbon atoms. The alkylor alkenyl group may be straight-chain or branched. However, thosehaving less than 6 or more than 30 carbon atoms are not preferredbecause they possibly deteriorate the function properties in a wetclutch.

[0042] Specific examples of the alkyl and alkenyl groups are alkylgroups, which may be straight-chain or branched, such as hexyl, heptyl,octyl, nonyl, decyl, undecyl, dodecyl (lauryl), tridecyl, tetradecyl(myristyl), pentadecyl, hexadecyl (palmityl), heptadecyl, octadecyl(stearyl), nonadecyl, eicosyl, heneicosyl, docosyl, tricosyl,tetracosyl, pentacosyl, hexacosyl, heptacosyl, octacosyl, nonacosyl andtriacontyl groups; and alkenyl groups, which may be straight-chain orbranched and the position of which the double bond may vary, such ashexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, dodecenyl,tridecenyl, tetradecenyl, pentadecenyl, hexadecenyl, heptadecenyl,octadecenyl (oleyl), nonadecenyl, eicosenyl, heneicosenyl, docosenyl,tricosenyl, tetracosenyl, pentacosenyl, hexacosenyl, heptacosenyl,octacosenyl, nonacosenyl and triacontenyl groups.

[0043] Preferred friction modifiers for the present invention are asfollows:

[0044] (C-1) an amine compound having in its molecules at least onealkyl or alkenyl group having 6 to 30 carbon atoms and no hydrocarbongroup having 31 or more carbon atoms, and derivatives thereof;

[0045] (C-2) a phosphorus compound having in its molecules at least onealkyl or alkenyl group having 6 to 30 carbon atoms and no hydrocarbongroup having 31 or more carbon atoms, and derivatives thereof; and

[0046] (C-3) an amide or metallic salt of a fatty acid having in itsmolecules at least one alkyl or alkenyl group having 6 to 30 carbonatoms and no hydrocarbon group having 31 or more carbon atoms.

[0047] Specific examples of (C-1) the amine compound are aliphaticmonoamines represented by the formula or alkyleneoxide adducts thereof

[0048] aliphatic polyamines represented by the formula

[0049] and imidazoline compounds represented by the formula

[0050] In formula (6), R¹⁰ is an alkyl or alkenyl group having 6 to 30,preferably 9 to 24 carbon atoms, R¹¹ and R¹² are each independentlyethylene or propylene, R¹³ and R¹⁴ are each independently hydrogen or ahydrocarbon group having 1 to 30 carbon atoms, f and g are eachindependently an integer of 0 to 10, preferably 0 to 6, and f+g=0 to 10,preferably 0 to 6.

[0051] In formula (7), R¹⁵ is an alkyl or alkenyl group having 6 to 30,preferably 9 to 24 carbon atoms, R¹⁶ is ethylene or propylene, R¹⁷ andR¹⁸ are each independently hydrogen or a hydrocarbon group having 1 to30 carbon atoms, h is an integer of 1 to 5, preferably 1 to 4.

[0052] In formula (8), R¹⁹ is an alkyl or alkenyl group having 6 to 30,preferably 9 to 24 carbon atoms, R²⁰ is ethylene or propylene, R²¹ ishydrogen or a hydrocarbon group having 1 to 30 carbon atoms, and i is aninteger of 0 to 10, preferably 0 to 6.

[0053] The alkyl or alkenyl group for R¹⁰, R¹⁵, and R¹⁹ may bestraight-chain or branched but have 6 to 30 carbon atoms, preferably 9to 24 carbon atoms.

[0054] Specific examples of the alkyl or alkenyl groups for R¹⁰, R¹⁵,and R¹⁹ are alkyl groups, which may be straight-chain or branched, suchas hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl (lauryl),tridecyl, tetradecyl (myristyl), pentadecyl, hexadecyl (palmityl),heptadecyl, octadecyl (stearyl), nonadecyl, eicosyl, heneicosyl,docosyl, tricosyl, tetracosyl, pentacosyl, hexacosyl, heptacosyl,octacosyl, nonacosyl and triacontyl groups; and alkenyl groups, whichmay be straight-chain or branched and the position of which the doublebond may vary, such as hexenyl, heptenyl, octenyl, nonenyl, decenyl,undecenyl, dodecenyl, tridecenyl, tetradecenyl, pentadecenyl,hexadecenyl, heptadecenyl, octadecenyl (oleyl), nonadecenyl, eicosenyl,heneicosenyl, docosenyl, tricosenyl, tetracosenyl, pentacosenyl,hexacosenyl, heptacosenyl, octacosenyl, nonacosenyl and triacontenylgroups. Among these, particularly preferred are alkyl or alkenyl groupshaving 12 to 18 carbon atoms, such as lauryl, myristyl, palmityl,stearyl, isostearyl (16-methylheptadecyl), and oleyl groups because theycan provide superior friction properties in a wet clutch.

[0055] Specific examples of the group for each R¹³, R¹⁴, R¹⁷, R¹⁸, andR²¹ are hydrogen; alkyl groups, which may be straight-chain or branched,such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl,nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl,hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, heneicosyl,docosyl, tricosyl, tetracosyl, pentacosyl, hexacosyl, heptacosyl,octacosyl, nonacosyl and triacontyl groups; alkenyl groups, which may bestraight-chain or branched and wherein the position of the double bondmay vary, such as butenyl, pentenyl, hexenyl, heptenyl, octenyl,nonenyl, decenyl, undecenyl, dodecenyl, tridecenyl, tetradecenyl,pentadecenyl, hexadecenyl, heptadecenyl, octadecenyl, nonadecenyl,eicosenyl, heneicosenyl, docosenyl, tricosenyl, tetracosenyl,pentacosenyl, hexacosenyl, heptacosenyl, octacosenyl, nonacosenyl andtriacontenyl groups; cycloalkyl groups having 5 to 7 carbon atoms, suchas cyclopentyl, cyclohexyl and cycloheptyl groups; alkylcycloalkylgroups, of which the alkyl group may bond to any position of thecycloalkyl group, having 6 to 11 carbon atoms, such asmethylcyclopentyl, dimethylcyclopentyl, methylethylcyclopentyl,diethylcyclopentyl, methylcyclohexyl, dimethylcyclohexyl,methylethylcyclohexyl, diethylcyclohexyl, methylcycloheptyl,dimethylcycloheptyl, methylethylcycloheptyl and diethylcycloheptylgroups; aryl groups such as phenyl and naphtyl groups; alkylaryl groups,of which the alkyl group may be straight-chain or branched and may bondto any position of the aryl group, having 7 to 18 carbon atoms, such astolyl, xylyl, ethylphenyl, propylphenyl, butylphenyl, pentylphenyl,hexylphenyl, heptylphenyl, octylphenyl, nonylphenyl, decylphenyl,undecylphenyl and dodecylphenyl groups; and arylalkyl groups, of whichthe alkyl group may be straight-chain or branched, having 7 to 12 carbonatoms, such as benzyl, phenylethyl, phenylpropyl, phenylbutyl,phenylpentyl and phenylhexyl groups.

[0056] Among the aliphatic monoamines of formula (6) and alkyleneoxideadducts thereof, more preferred are those of formula (6) wherein R¹³ andR¹⁴ are each independently hydrogen or an alkyl group having 1 to 6carbon atoms, and f=g=0, and alkyleneoxide adducts of aliphaticmonoamines of formula (6) wherein both R¹³ and R¹⁴ are hydrogen, and fand g are each independently an integer of 0 to 6 and f+g=1 to 6 becauseof their good friction properties in a wet clutch.

[0057] Among the aliphatic polyamines of formula (7), preferred arethose of formula (7) wherein R¹⁷ and R¹⁸ are each independently hydrogenor an alkyl group having 1 to 6 carbon atoms because of their goodfriction properties in a wet clutch.

[0058] Among the imidazoline compounds of formula (8), preferred arethose of formula (8) wherein R²¹ is hydrogen or an alkyl group having 1to 6 carbon atoms because of their good friction properties in a wetclutch.

[0059] First examples of derivatives of the amine compounds alsoreferred to as (C-1) are acid-modified compounds obtained by allowingthe above-described amine compound of formula (6), (7) or (8) to reactwith monocarboxylic acid (aliphatic acid) having 2 to 30 carbon atoms orpolycarboxylic acid having 2 to 30 carbon atoms, such as oxalic acid,phthalic acid, trimellitic acid, and pyromellitic acid so as toneutralize the whole or part of the remaining amino and/or imino groupsor to convert the whole or part of the same into amide. Second examplesare boron-modified compounds obtained by allowing the above-describedamine compound of formula (6), (7) or (8) to react with boric acid so asto neutralize the whole or part of the remaining amino and/or iminogroups. Third examples are salts of phosphates obtained by allowing theabove-described amine compound of formula (6), (7) or (8) to react withacid phosphate or acid phosphite each having in its molecules one or twohydrocarbon groups having 1 to 30 carbon atoms but no hydrocarbon grouphaving 31 or more carbon atoms and having at least one hydroxyl group soas to neutralize the whole or part of the remaining amino or iminogroups. Forth examples are alkyleneoxide adducts of amine compoundsobtained by allowing the amine compound of formula (7) or (8) to reactwith an alkylene oxide such as ethylene oxide and propylene oxide. Otherthan these compounds, there may be used modified products obtained bysubjecting the amine compound of formula (6), (7), or (8) to two or moreof the aforesaid modifications.

[0060] Therefore, in view of the capability to provide excellentfriction properties in a wet clutch, preferred amine compound andderivatives thereof referred to as Component (C-1) are as follows:

[0061] (i) amine compounds such as lauryl amine, lauryl diethylamine,lauryl diethanolamine, dodecyldipropanolamine, palmitylamine,stearylamine, stearyltetraethylenepentamine, oleylamine,oleylpropylenediamine, oleyldiethanolamine, and

[0062] N-hydroxyethyloleylimidazolyne;

[0063] (ii) alkyleneoxide adducts of the above amine compounds (i);

[0064] (iii) salts of the above amine compounds (i) and acid phosphatesuch as di-2-ethylhexylphosphate or acid phosphite such as2-ethylhexylphosphite;

[0065] (iv) boric acid-modified product of the above amine compounds(i), the above alkyleneoxide adducts (ii) or the salts (iii); and

[0066] (v) mixtures of any two or more of (i), (ii), (iii), and (iv).

[0067] Phosphorus compounds referred to as Component (C-2) arephosphates represented by the formula

[0068] and

[0069] phosphites represented by the formula

[0070] In formula (9), R²² is an alkyl or alkenyl group having 6 to 30,9 to 24 carbon atoms, R²³ and R²⁴ are each independently hydrogen or ahydrocarbon group having 1 to 30 carbon atoms, F¹, F², F³, and F⁴ areeach independently oxygen or sulfur, provided that at least one of F¹,F², F³, and F⁴ is oxygen.

[0071] In formula (10), R²⁵ is an alkyl or alkenyl group having 6 to 30,preferably 9 to 24 carbon atoms, R²⁶ and R²⁷ are each independentlyhydrogen or a hydrocarbon group having 1 to 30 carbon atoms, F⁵, F⁶, andF⁷ are each independently oxygen or sulfur provided that at least one ofF⁵, F⁶, and F⁷ is oxygen.

[0072] The alkyl and alkenyl group for R²² and R²⁵ may be straight-chainor branched ones but have 6 to 30, preferably 9 to 24 carbon atoms.Departures from the above-specified range of carbon number would cause adeterioration in friction properties in a wet clutch.

[0073] Specific examples of the alkyl or alkenyl groups for R²² and R²⁵are alkyl groups, which may be straight-chain or branched, such ashexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl (lauryl), tridecyl,tetradecyl (myristyl), pentadecyl, hexadecyl (palmityl), heptadecyl,octadecyl (stearyl), nonadecyl, eicosyl, heneicosyl, docosyl, tricosyl,tetracosyl, pentacosyl, hexacosyl, heptacosyl, octacosyl, nonacosyl andtriacontyl groups; and alkenyl groups, which may be straight-chain orbranched and the position of which the double bond may vary, such ashexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, dodecenyl,tridecenyl, tetradecenyl, pentadecenyl, hexadecenyl, heptadecenyl,octadecenyl (oleyl), nonadecenyl, eicosenyl, heneicosenyl, docosenyl,tricosenyl, tetracosenyl, pentacosenyl, hexacosenyl, heptacosenyl,octacosenyl, nonacosenyl and triacontenyl groups. Among these,particularly preferred are straight-chain alkyl or alkenyl groups having12 to 18 carbon atoms, such as lauryl, myristyl, palmityl, stearyl, andoleyl groups with because they can provide superior friction propertiesin a wet clutch.

[0074] Specific examples of the hydrocarbon group for R²³, R²⁴, R²⁶, andR²⁷ are alkyl groups, which may be straight-chain or branched, such asmethyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl,decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl,heptadecyl, octadecyl, nonadecyl, eicosyl, heneicosyl, docosyl,tricosyl, tetracosyl, pentacosyl, hexacosyl, heptacosyl, octacosyl,nonacosyl and triacontyl groups; alkenyl groups, which may bestraight-chain or branched and wherein the position of the double bondmay vary, such as butenyl, pentenyl, hexenyl, heptenyl, octenyl,nonenyl, decenyl, undecenyl, dodecenyl, tridecenyl, tetradecenyl,pentadecenyl, hexadecenyl, heptadecenyl, octadecenyl, nonadecenyl,eicosenyl, heneicosenyl, docosenyl, tricosenyl, tetracosenyl,pentacosenyl, hexacosenyl, heptacosenyl, octacosenyl, nonacosenyl andtriacontenyl groups; cycloalkyl groups having 5 to 7 carbon atoms, suchas cyclopentyl, cyclohexyl and cycloheptyl groups; alkylcycloalkylgroups, of which the alkyl group may bond to any position of thecycloalkyl group, having 6 to 11 carbon atoms, such asmethylcyclopentyl, dimethylcyclopentyl, methylethylcyclopentyl,diethylcyclopentyl, methylcyclohexyl, dimethylcyclohexyl,methylethylcyclohexyl, diethylcyclohexyl, methylcycloheptyl,dimethylcycloheptyl, methylethylcycloheptyl and diethylcycloheptylgroups; aryl groups such as phenyl and naphtyl groups; alkylaryl groups,of which the alkyl group may be straight-chain or branched and may bondto any position of the aryl group, having 7 to 18 carbon atoms, such astolyl, xylyl, ethylphenyl, propylphenyl, butylphenyl, pentylphenyl,hexylphenyl, heptylphenyl, octylphenyl, nonylphenyl, decylphenyl,undecylphenyl and dodecylphenyl groups; and arylalkyl groups, of whichthe alkyl group may be straight-chain or branched, having 7 to 12 carbonatoms, such as benzyl, phenylethyl, phenylpropyl, phenylbutyl,phenylpentyl and phenylhexyl groups.

[0075] Because their excellent friction properties in a wet clutch,preferred phosphorus compounds as Component (C-2) are acid phosphatesrepresented by formula (9) wherein at least one of R²³ and R²⁴ ishydrogen and acid phosphites represented formula (10) wherein at leastone of R²⁶ and R²⁷ is hydrogen.

[0076] Specific examples of the derivatives of the phosphoric compoundsalso referred to as Component (C-2) are salts obtained by allowing anacid phosphite of formula (9) wherein at least one of R²³ and R²⁴ ishydrogen or an acid phosphite of formula (10) wherein at least one ofR²⁶ and R²⁷ is hydrogen to react with a nitrogen-containing compoundsuch as ammonia or an amine compound having in its molecules onlyhydrocarbon or hydroxyl-containing groups having 1 to 8 carbon atoms soas to neutralize the whole or part of the remaining acid hydrogen.

[0077] Specific examples of such a nitrogen-containing compound areammonia; alkylamines, of which the alkyl group may be straight-chain orbranched, such as monomethylamine, monoethylamine, monopropylamine,monobutylamine, monopentylamine, monohexylamine, monoheptylamine,monooctylamine, dimethylamine, methylethylamine, diethylamine,methylpropylamine, ethylpropylamine, dipropylamine, methylbutylamine,ethylbutylamine, propylbutylamine, dibutylamine, dipentylamine,dihexylamine, diheptylamine and dioctylamine; alkanolamines, of whichthe alkanol group may be straight-chain or branched, such asmonomethanolamine, monoethanolamine, monopropanolamine,monobutanolamine, monopentanolamine, monohexanolamine,monoheptanolamine, monooctanolamine, monononanolamine, dimethanolamine,methanolethanolamine, diethanolamine, methanolpropanolamine,ethanolpropanolamine, dipropanolamine, methanolbutanolamine,ethanolbutanolamine, propanolbutanolamine, dibutanolamine,dipentanolamine, dihexanolamine, diheptanolamine and dioctanolamine; andmixtures thereof.

[0078] Because of their excellent friction properties in a wet clutch,particularly preferred phosphorus compounds as Component (C-2) aremonolauryl phosphate, dilauryl phosphate, monostearyl phosphate,distearyl phosphate, monooleyl phosphate, dioleyl phosphate, monolaurylphosphate, dilauryl phosphite, monostearyl phosphite, distearylphosphite, monooleyl phosphite, dioleylphosphite, monolaurylthiophosphate, dilauryl thiophosphate, monostearyl thiophosphate,distearyl thiophosphate, monooleyl thiophosphate, dioleyl thiophosphate,monolauryl thiophosphate, dilauryl thiophosphite, monostearylthiophosphite, distearyl thiophosphite, monooleyl thiophosphite, dioleylthiophosphite; amine salts of these phosphates such asmono2-ethylhexylamine salts, phosphite, thiophosphate and thiophosphite;and mixtures thereof.

[0079] The fatty acid amide or fatty metal salt referred to as Component(C-3) may be straight-chain or branched and saturated or unsaturatedfatty acids but the alkyl group or alkenyl group thereof has 6 to 30,preferably 9 to 24 carbon atoms. Fatty acids having an alkyl or alkenylgroup having fewer than 6 or 31 or greater carbon atoms are notpreferred because they would cause the deterioration of frictionproperties in a wet clutch.

[0080] Specific examples of the fatty acid are straight-chain orbranched saturated fatty acids, such as heptanoic acid, octanonic acid,nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid,tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoicacid, heptadecanoic acid, octadecanoic acid; nonadecanoic acid,icosanoic acid, henicosanoic acid, docosanoic acid, tricosanoic acid,tetracosanoic acid, pentacosanoic acid, hexacosanoic acid, heptacosanoicacid, octacosanoic acid, nonacosanoic acid, and triacontanoic acid; andstraight-chain or branched unsaturated fatty acids, wherein the positionthe double bond may vary, such as heptanoic acid, octenoic acid,nonenoic aicd, decenoic acid, undecenoic acid, dodecenoic acid,tridecenoic acid, tetradecenoic acid, pentadecenoic acid, hexadecenoicacid, heptadecenoic acid, octadecenoic acid, nonadecenoic acid,eicosenoic acid, heneicosenoic acid, docosenoic acid, tricosenoic acid,tetracosenoic acid, pentasenoic acid, hexacosenoic acid, heptacosenoicacid, octacosenoic acid, nonacosenoic acid and triacontenoic acid.Because of their excellent friction properties in a wet clutch,particularly preferred fatty acids are straight-chain fatty acidsderived from various types of fats and oils such as lauric acid,myristic acid, palmitic acid, stearic acid and oleic acid and mixturesof straight-chain fatty acid and branched fatty acid obtained by the oxosynthesis.

[0081] The fatty acid amide referred to as Component (C-3) may be amidesobtained by reacting a nitrogen-containing compound such as ammonia andamine compound having per molecule only hydrocarbon orhydroxyl-containing hydrocarbon groups having 1 to 8 carbon atoms.

[0082] Specific examples of such a nitrogen-containing compound areammonia; alkylamine, of which the alkyl group may be straight-chain orbranched, such as monomethylamine, monoethylamine, monopropylamine,monobutylamine, monopentylamine, monohexylamine, monoheptylamine,monooctylamine, dimethylamine, methylethylamine, diethylamine,methylpropylamine, ethylpropylamine, dipropylamine, methylbutylamine,ethylbutylamine, propylbutylamine, dibutylamine, dipentylamine,dihexylamine, diheptylamine and dioctylamine; and alkanolamines, ofwhich the alkanol group may be straight-chain or branched, such asmonomethanolamine, monoethanolamine, monopropanolamine,monobutanolamine, monopentanolamine, monohexanolamine,monoheptanolamine, monooctanolamine, monononanolamine, dimethanolamine,methanolethanolamine, diethanolamine, methanolpropanolamine,ethanolpropanolamine, dipropanolamine, methanolbutanolamine,ethanolbutanolamine, propanolbutanolamine, dibutanolamine,dipentanolamine, dihexanolamine, diheptanolamine, and dioctanolamine.

[0083] Because of their excellent friction properties in a wet clutch,specific examples of the fatty acid amides as Component (C-3) are lauricacid amide, lauric acid diethanolamide, lauric monopropanolamide,myristic acid amide, myristic acid diethanolamide, myristic acidmonopropanolamide, palmitic acid amide, palmitic acid ethanolamide,palmitic acid monopropanolamide, stearic acid amide, stearic aciddiethanolamide, stearic acid monopropanolamide, oleic acid amide, oleicacid diethanolamide, oleic acid monopropanol amide, coconut oil fattyamide, coconut oil fatty acid diethanolamide, coconut oil fattymonopropanolamide, synthetic mixed fatty amides having 12 to 13 carbonatoms, synthetic mixed fatty diethanolamides having 12 to 13 carbonatoms, synthetic mixed fatty monopropanolamides having 12 to 13 carbonatoms, and mixtures thereof.

[0084] Specific examples of the fatty metallic acid also referred to asComponent (C-3) are alkaline earth metal salts such as a magnesium saltand a calcium salt, and a zinc salt of any of the above-exemplifiedfatty acids. Because of their excellent friction properties in a wetclutch, particularly preferred fatty acid metallic salts are calciumlaurate, calcium myristate, calcium palmitate, calcium stearate, calciumoleate, coconut oil fatty acid calcium, synthetic mixed fatty acidcalcium having 12 or 13 carbon atoms, zinc laurate, zinc myristate, zincpalmitate, zinc stearate, zinc oleate, coconut oil fatty zinc, syntheticmixed fatty zinc having 12 to 13 carbon atoms, and mixtures thereof.

[0085] Any one or more members arbitrary selected from theabove-described Components (C-1) through (C-3) may be added to thetransmission lubricant composition of the present invention in anysuitable amount as long as they do not adversely affect the otherproperties of the resulting composition such as oxidation stability. Inorder to obtain long-lasting friction properties of the composition, itis necessary to avoid a deterioration in friction properties caused bythe deterioration of the friction modifier. Addition of large amounts ofComponent (C) is effective in obtaining long-lasting frictionproperties. However, too large amounts of Component (C) would lead toreduced static friction coefficient which is required to be high so asto maintain the coupling or engagement of a wet clutch. The amount ofComponent (C) is thus limited to some extent.

[0086] Therefore, the content of Component (C) is within the range ofpreferably 0.005 to 3.0 mass percent, preferably 0.01 to 2.0 masspercent, based on the total mass of the transmission lubricantcomposition of the present invention.

[0087] The transmission lubricant composition of the present inventionis obtained by blending a particular mineral base oil with suitableamounts of the viscosity index improver and friction modifier. Althoughthe composition as such is superior in the durability of anti-shudderproperties and in low temperature fluidity, in order to further enhancesuch properties there may be blended various additives such as anti-wearagents, extreme pressure agents, ashless dispersants, metallicdetergents, oxidation inhibitors, corrosion inhibitors, anti-foamingagents and dyes. These additives may be used individually or incombination.

[0088] Anti-wear agents may be any of conventional ones for lubricants.Eligible abrasion inhibitors are one or more phosphorus compounds suchas salts of monophosphates, diphosphates, triphosphates, monophosphites,diphosphites, triphosphites, or these esters with amines oralkanolamines. The content of such abrasion inhibitors is selected fromthe range of 0.005 to 2 percent by mass, based on the total mass of thetransmission lubricant composition.

[0089] Extreme pressure agents may be any of conventional ones forlubricants. Eligible extreme pressure agents are sulfuric compounds suchas disulfides, olefin sulfides, and sulfurized fats and oils. One ormore of these compounds is preferably added in an amount of 0.1 to 5.0percent by mass based on the total mass of the transmission lubricantcomposition.

[0090] Ashless dispersants may be any of conventional ones forlubricants, such as amino- or imino-compounds having their molecules atleast one alkyl or alkenyl group having 40 to 400 carbon atoms, andmodified products thereof.

[0091] The alkyl and alkenyl groups may be straight-chain or branched.Preferred are branched alkyl and alkenyl groups derived from oligomersof olefins such as propylene, 1-butne, and isobutylene or cooligomers ofethylene and propylene. The alkyl and alkenyl groups have preferably 60to 350 carbon atoms. Alkyl and alkenyl groups having fewer than 40carbon atoms would result in a compound having poor solubility to thelubricating base oil, those having over 400 carbon atoms woulddeteriorate the low temperature fluidity of the transmission lubricantcomposition.

[0092] Examples of derivatives of the amino and/or imino compounds are(i) acid-modified compounds obtained by allowing the above-describedamino or imino compound to react with monocarboxylic acid having 2 to 30carbon atoms, such as fatty acid or polycarboxylic acid having 2 to 30carbon atoms, such as oxalic acid, phthalic acid, trimellitic acid, andpyromellitic acid to neutralize the whole or part of the remaining aminoand/or imino groups or to convert the whole or part of the same intoamide; (ii) boron-modified compounds obtained by allowing theabove-described amino or imino compound to react with boric acid toneutralize the whole or part of the remaining amino and/or imino groupsor to convert the whole or part of the same into amide; and (iii)sulfur-modified compounds obtained by allowing the above-described aminoor imino compound to react with a sulfuric compound.

[0093] There may be blended the above-described amino and iminocompounds and one or more modified products thereof as the ashlessdispersant. The content thereof is selected from the range of 0.1 to 10percent by mass, based on the total mass of the transmission lubricantcomposition.

[0094] Metallic detergents may be any of conventional ones forlubricants. Eligible metallic detergents are sulfonates, phenates, andsalicylates of alkaline metals or alkaline earth metals. These compoundsmay be used individually or in combination. Examples of the alkalinemetals are sodium and potassium, while examples of the alkaline earthmetals are calcium and magnesium. Specific examples of the metallicdetergent are sulfonates, phenates and salicylates of calcium ormagnesium.

[0095] The content of the metallic detergent is arbitrary selected,depending on the properties required for the transmission lubricantcomposition. In general, the metallic detergent is blended in an amountof 0.1 to 5.0 percent by mass, based on the total mass of thetransmission lubricant composition.

[0096] Oxidation inhibitors are any of conventional ones for lubricants.Eligible oxidation inhibitors are phenol- or amine-based compounds.These may be used individually or in combination. Specific examples ofthe oxidation inhibitor are alkylphenols such as2-6-di-tert-butyl-4-methylphenol, bisphenols such asmethylene-4,4-bisphenol(2,6-di-tert-butyl-4-methylphenol), naphtylaminessuch as phenyl-α-naphtylamine, dialkyldiphenylamines, zincdialkyldithiophosphates such as zinc di-2-ethylhexyldithiophosphate,esters of 3,5-di-tert-butyl-4-hydroxyphenyl fatty acid (propionic acid)with a mono- or poly-hydric alcohol such as methanol, octadecanol, 1,6hexanediol, neopentyl glycol, thiodiethylene glycol, triethylene glycolor pentaerythritol.

[0097] The oxidation inhibitor is blended in an amount of 0.01 to 5.0percent by mass based on the total mass of the transmission lubricantcomposition.

[0098] Corrosion inhibitors may be conventional ones for lubricants.Eligible corrosion inhibitors are benzotriazole-, tolyltriazole-,thiodiazole- and imidazole-based compounds. These may be usedindividually or in combination. The corrosion inhibitor is usuallyblended in an amount of 0.01 to 3.0 percent by mass, based on the totalmass of the transmission lubricant composition.

[0099] Anti-foaming agents may conventional ones for lubricants.Eligible anti-foaming agents are silicones such as dimethylsilicon andfluorosilicon. These may be used individually or in combination. Theanti-foaming agents is usually blended in an amount of 0.001 to 0.05percent by mass, based on the total mass of the transmission lubricantcomposition.

[0100] When a dye is blended in the lubricant composition of the presentinvention, they may be conventional ones. The dye is usually blended inan amount of 0.001 to 1.0 percent by mass, based on the total mass ofthe transmission lubricant composition.

[0101] The invention will be further described by way of the followingexamples and comparative examples which are provided for illustrativepurposes only.

[0102] EXAMPLES

[0103] Transmission lubricant compositions of the present invention andof comparative examples were prepared such that the kinematic viscosityat 100 ° C. of each composition is made to 7.3 mm²/s, in accordance withthe formulations indicated in Table 1.

[0104] Each of the compositions was subjected to an anti-shudderdurability test, a low temperature viscosity measurement, and a shearstability test. Table 1 shows the results of the durability ofanti-shudder properties, low temperature fluidity, and shear stability.TABLE 1 Compara- Inventive Examples tive 1 2 3 4 Example 1 Base OilMineral Oil A¹⁾ mass % 79 55.3 12.3 79 — Mineral Oil B²⁾ mass % — 11.975.7 — — Mineral Oil C³⁾ mass % — 11.8 — — 44.9 Mineral Oil D⁴⁾ mass % —— — — 35.3 Kinematic Viscosity mm²/s 2.8 2.8 3.8 2.8 2.8 of Base Oil(100° C.) % C_(P) of Base Oil 76 75 81 76 62 % C_(A) of Base Oil 2 2 0.62 5.6 Viscosity Index mass % — — — 15 — Improver A⁵⁾ Viscosity Indexmass % 15 15 — — 13.8 Improver B⁶⁾ Viscosity Index mass % — — 6.4 — —Improver C⁷⁾ Ashless Dispersant mass % 3 3 3 3 3 A⁸⁾ Ashless Dispersantmass % 1 1 0.5 1 1 B⁹⁾ Anti-wear agent¹⁰⁾ mass % 0.2 0.2 0.2 0.2 0.2Ca-based mass % 0.4 0.4 0.5 0.4 0.4 Detergent¹¹⁾ Oxidation Inhibitormass % 0.5 0.5 0.5 0.5 0.5 A¹²⁾ Oxidation Inhibitor mass % 0.5 0.5 0.50.5 0.5 B¹³⁾ Friction Modifier mass % 0.1 0.1 0.1 0.1 0.1 A¹⁴⁾ FrictionModifier mass % 0.2 0.2 0.2 0.2 0.2 B¹⁵⁾ Corrosion mass % 0.1 0.1 0.10.1 0.1 Inhibitor¹⁶⁾ Low temperature mPa · s 8300 8300 16200 8100 20400Viscosity (−40° C.) The time taken until h 144 144 168 120 48 dμ/dVreached less than 0 Viscosity reduction % 4.8 4.8 14.2 4.8 4.3 aftershear

Anti-Shudder Durability Test

[0105] The results of μ-V characteristics evaluation test using a wetclutch was used as a measure of the anti-shudder properties of atransmission lubricant composition. The α-V characteristics wasevaluated in accordance with “Test method for anti-shudder performanceof automatic transmission fluids” prescribed in JASO M349-98. Atransmission lubricant composition is considered to have no anti-shudderproperties in the case where dμ/dV(50) or d μ/dV(1 50) defined by theformulae below is less than 0.

dμ/dV(50)=(μ₅₀−μ₁)/(V ₅₀ −V ₁)

dμ/dV(150)=(μ₁₅₀−μ₅₀)/(V ₁₅₀ −V ₅₀)

[0106] wherein μ₁ is friction coefficient at 1 rpm,

[0107] μ₅₀ is friction coefficient at 50 rpm,

[0108] μ₁₅₀ is friction coefficient at 150 rpm,

[0109] V₁ is a sliding velocity of 0.006 m/s at 1 rpm,

[0110] V₅₀ is a sliding velocity of 0.3 m/s at 50 rpm,

[0111] V₁₅₀ is a sliding velocity of 0.9 m/s at 150 rpm.

[0112] Each of the above lubricant compositions was subjected to “Testmethod for Oxidation Stability of Lubricating Oils for InternalCombustion Engines” of “Testing Methods for Oxiation Stability ofLubricating Oils” prescribed in JIS K2514-1993, at a test temperature of150° C., for varied test periods of time, thereby preparing variousdeteriorated oils. The μ-V characteristics of each deteriorated oil wasevaluated. Anti-shudder durability was determined by the time takenuntil dμ/dV(50) or dμ/dV(150) reached less than 0.

Low Temperature Viscosity Evaluation

[0113] The low temperature viscosity at -40° C. of each transmissionlubricant composition was measured in a low temperature liquid bath inaccordance with “Gear oil low temperature viscosity determinationmethod” prescribed in JPI-5S-26-85.

Shear Stability Test

[0114] Each of the above transmission lubricant composition wasirradiated with ultrasonic wave for one hour in accordance with “Testmethod for shear stability of automatic transmission fluids” prescribedin JASO M347-95. The viscosity reduction rate of each composition wasderived from the kinematic viscosity of before and after irradiationusing the following equation:

ΔV=(V ₀ −V _(r))/V ₀×100

[0115] wherein ΔV is viscosity reduction rate (% )

[0116] V₀ is kinematic viscosity (mm²/s) before irradiation

[0117] V_(r) is kinematic viscosity (mm²/s) after irradiation

[0118] As apparent from the results shown in Table 1, the transmissionlubricant compositions of Examples 1 to 4 take longer time until dμ/t/dVvalues reached 0 and have excellent properties, i.e., low viscosity atlow temperatures.

[0119] Whereas, the transmission lubricant composition of ComparativeExample 1 contains a base oil of which % C_(P) and/or % C_(A) deviatesthe ranges defined by the present invention and thus take shorter timeuntil dμ/dV values reached 0 with less durable in anti-shudderproperties and high viscosity at low temperatures.

What is claimed is:
 1. A transmission lubricant composition whichcomprises a mineral oil as a base oil of which % CP and % C_(A) definedin ASTM D 3238 are 70 or more and 3 or less, respectively, a viscosityindex improver, and a friction modifier.
 2. The transmission lubricantcomposition according to claim 1 wherein said viscosity index improveris selected from the group consisting of various polymethacrylates. 3.The transmission lubricant composition according to claim 2 wherein saidpolymethacrylates have a weight-average molecular weight of 10,000 to200,000.
 4. The transmission lubricant composition according to claim 1wherein said mineral oil has a kinematic viscosity at 100° C. of 1 to 10mm²/s.
 5. The transmission lubricant composition according to claim 1wherein said viscosity index improver is selected from the groupconsisting of dispersion type viscosity index improvers.